Field of the Invention
The present invention relates to an imprint method, an imprint apparatus, and an article manufacturing method.
Description of the Related Art
As the demand for microfabrication of semiconductor devices or MEMS increases, not only has conventional photolithography technology, but also, microfabrication technology, in which an uncured resin on a substrate is molded by a mold to thereby form a resin pattern on the substrate, has been receiving attention. This technology is also referred to as “imprint technology”, by which a fine structure with dimensions of a few nanometers can be formed on a substrate. One example of the imprint technology includes a photo-curing method. An imprint apparatus employing the photo-curing method first applies an ultraviolet curable resin (imprint material, photocurable resin) to a shot (imprint region) on a substrate (wafer). Next, the resin (uncured resin) is molded by a mold. After the ultraviolet curable resin is irradiated with ultraviolet light for curing, the cured resin is released from the mold, whereby a resin pattern is formed on the substrate.
Here, in a series of device manufacturing steps, heat processing in a film formation step, such as sputtering, is performed for a substrate to be subjected to imprint processing. Consequently, the entire substrate may be expanded or reduced, resulting in a change in the shape (size) of the pattern in the direction of two orthogonal in-plane axes. Thus, in an imprint apparatus, the shape of the substrate-side pattern formed on a substrate needs to be matched with the shape of the pattern section formed on a mold when the mold is pressed against the resin on the substrate. In a conventional exposure apparatus, such shape correction (magnification correction) can be ensured by changing the size of each shot during exposure processing by changing the reduction magnification of a projection optical system in accordance with the magnification of the substrate or by changing the scanning speed of a substrate stage. However, the imprint apparatus does not have a projection optical system and the mold is brought into direct contact with the resin on the substrate, and thus, it is difficult to perform such correction. Hence, the imprint apparatus employs a shape correction mechanism (magnification correction mechanism) that physically deforms a mold by imparting an external force to the sides of the mold or by expanding the mold by heating.
For example, assume a case wherein the imprint apparatus is applied to a manufacturing step of manufacturing a semiconductor device having a half-pitch of about 32 nm. At this time, according to ITRS (International Technology Roadmap for Semiconductors), the superposition accuracy is 6.4 nm. In order to accommodate this, shape correction also needs to be performed with an accuracy of a few nm or less. On the other hand, the mold (pattern section) used in the imprint apparatus may also be distorted by the following causes. For example, the pattern surface of a mold is directed upward when the mold is being prepared, whereas the pattern surface thereof is directed downward when the mold is used (during pressing). Thus, the pattern section may be deformed upon usage under the influence of gravity. Although the pattern section is typically formed by a drawing apparatus using an electron beam, or the like, the pattern section may also be distorted due to distortion aberration of the optical system of the drawing apparatus during formation thereof. Furthermore, even if the pattern section can be prepared without distortion, the occurrence of distortion in a substrate-side pattern may result in an adverse effect on the superposition accuracy. Accordingly, in order to suppress such distortion (deformation) of the mold and to improve superposition accuracy, Japanese Patent Laid-Open No. 2004-259985 discloses a pattern forming apparatus that controls the temperature of a mold and a substrate by means of a retention temperature control unit, and corrects the shape of the mold or the substrate by generating desired thermal deformation in the mold or the substrate.
In the conventional imprint apparatus, however, a substrate is held by a substrate holding unit, such as a wafer chuck, with the bottom surface of the substrate restricted thereto. Thus, even if thermal deformation is generated on the substrate under temperature control disclosed in Japanese Patent Laid-Open No. 2004-259985, it is still difficult to sufficiently change the shape of the substrate-side pattern relative to the shape of the pattern section. Accordingly, an imprint apparatus is desired that is capable of improving superposition accuracy between a mold and a resin on a substrate by readily implementing not only the correction of the shape of the mold, but also, the correction of the shape of the substrate (including the substrate-side pattern) relative to the shape of the mold.